Some radar apparatuses have a function of controlling a gain of a reception signal in accordance with their purposes. A general function of this type is STC (Sensitivity Time control). In STC, the law that the strength of an echo reflected from a target is inversely proportional to the fourth power of the distance from the target is utilized. For example, for detection of a target in a short range, a receiver sensitivity is suppressed by decreasing a gain within the bounds of not losing track of the target, and for detection of a target in a long range, the receiver sensitivity is increased by increasing the gain as the distance increases. The STC makes it possible to normally receive an echo reflected from a target in a short range, and prevent an echo reflected from a terrain, building or surface of the sea (collectively referred to as clutter) from interfering with the reception of an echo reflected from a target in a long range.
To realize the above-described STC, a radar apparatus comprising a receiving unit for short-range detection and a receiving unit for long-range detection has been proposed (see, Jpn. Pat. Appln. KOKAI Publication No. 2008-72506, for example). The radar apparatus realizes short-range detection and long-range detection by selective switching between the receiving unit for short-range detection and the receiving unit for long-range detection. However, this radar apparatus requires a plurality of receiving units, and involves a problem that costs and size of the entire radar apparatus are inevitably increased.
To realize the STC, a radar apparatus in which a gain processing path for short-range detection and a gain processing path for long-range detection are connected to a single receiver has also been proposed (see, Jpn. Pat. Appln. KOKAI Publication No. 2007-170845, for example). This radar apparatus detects, by means of a timing controller, a time when switching between a short-range detection mode and a long-range detection mode is performed, and performs switching between the gain processing path for short-range detection and the gain processing path for long-range detection at the detected time. Then, the radar apparatus processes a signal which has passed the gain processing path for short-range detection or long-range detection by means of the single receiver. However, the radar apparatus requires the timing controller which detects a time at which switching between the short-range detection mode and the long-range detection mode is performed. The timing controller is expensive, and the use of the timing controller results in higher costs of the radar apparatus.